The problem of disposing of municipal and industrial waste has been recognized for many years. As a result, a number of approaches combined various waste materials with cement. For example a U.S. Pat. No. 4,678,514 of Deyhle et al. discloses a process for the disposal of combustible refuses. The process disposes a combustible refuse in the manufacture of clinker by preheating the partly calcining the cement raw meal in a preheater, burning in a rotary kiln and subsequently air cooling the clinker, the refuse being separately burned and the flue gas obtained thereby transfers its heat to the cement raw meal. In the process according to the invention, hot exhaust air from the clinker cooler is fed to the refuse incinerator and flue gas having a temperature of from 1000° to 1400° C., is produced during said incineration by means of which the cement raw meal is calcined. The slag of the refuse incineration is separately discharged.
A more recent approach to an environmental friendly utilization of asbestos-cement products are disclosed in a U.S. Pat. No. 5,676,750 of Gleichmar et al. The process includes a thermal process to transform the asbestos component. Inventively, this is achieved by a course reduction of the asbestos-cement products under black side conditions with maintained vacuum. Then, the material is ground to asbestos-cement meal and fed to the flame zone of the rotary kiln of a cement clinker production line. Depending on the fuel type used the portion of fed asbestos-cement meal varies between 2 and 5%, related to the amount of cement raw meal, substituting 2 to 5% of the cement raw meal mix at a time. The thermal transformation of the asbestos component takes place with temperatures of approximately 1800° C. in the burner zone. The modified residual substance becomes a constituent of the cement clinker due to assimilation in the kiln charge.
A further approach to waste disposal is taught by a U.S. Pat. No. 7,037,368 of Hoffis. The Hoffis patent describes a mid-kiln injection of waste-derived materials for the production of cement clinker. The method comprises the steps of introduction of non-traditional materials into the kiln, preferably at a mid-kiln location. The non-traditional materials are materials that are difficult, expensive or environmentally challenging for disposal. In one embodiment, weathered clinker is introduced into the kiln to admix with the raw material mix to augment clinker production. In another embodiment, bird, animal or human manure is added to the kiln so that the gaseous reducing agents can be released by the manure and combine with certain noxious gases generated during the clinker production to thereby reduce the noxious gas output. In another embodiment, other non-traditional waste-derived fuels are added to the kiln during clinker production, including railroad ties coated with creosote, industrial, commercial and consumer rubber components, such as rubber hoses, unshredded plastics and organic materials, such as bird and animal meal.
In addition, a U.S. Pat. No. 7,128,780 of Matheson et al. discloses a process for producing building materials, such as asphalt, cement, concrete, mortar, or plaster board from liquid paint sludge containing water and paint solids produced from overspray in commercial paint booth operations. The preferred embodiment comprises adding the liquid paint sludge as the hydrating agent directly to the building material mix.
Notwithstanding the above, it is presently believed that there is a need for and a potential commercial market for an environmentally compatible cement composition and method for making the same in accordance with the present invention. There should be a commercial market for such compositions and methods because a lower firing temperature of the kiln reduces the use of energy, uses less fossil fuels and offers an opportunity to capture the CO2 gases produced from heating magnesium. In addition, the heating process produces reactive chemical salts that are added to a predetermined, but variable amount of hydraulic cement and if desired reactive waste. The result is an environmental friendly cement that when blended with water and aggregates such as sand or gravel, placed in molds and cast into blocks or other structures.